The invention relates to an air-spring leg having a telescopic element which is preferably in the form of a shock absorber and which comprises a cylinder, a piston retractable therein, and an air chamber of variable volume which is combined with the telescopic element and is surrounded by a first casing part connected for wobbling movement to the piston, by a second casing part fastened to the cylinder and by a bellows arranged between the casing parts, and which substantially concentrically surrounds the telescopic element, at least over an axial portion, while the one casing part has a diameter smaller than that of the other casing part and is axially retractable into the other casing part during inward spring strokes.
Air-spring legs of this type are known, for example, from German Patent Document DE 34 45 984 A1. In the case of vehicle springs, the casing part connected for wobbling movement to the piston or its piston rod is usually fastened to the chassis or the body of the vehicle, so that, during suspension strokes, more or less large wobbling movements can occur between this casing part and the telescopic element if, during suspension strokes, the telescopic element fastened between the chassis or vehicle body and the axle or wheel makes swivelling movements relative to the chassis or vehicle body.
In air-spring legs of this kind, the casing part on the cylinder side is fixed to the cylinder, so that, when swivelling movements of the telescopic element relative to the vehicle body or chassis are made, distinct radial movements occur between the casing parts. The bellows must accordingly permit great movability of the casing parts relative to one another in the radial direction.
German Patent Document DE 40 10 982 A1 describes a spring leg in which the air-spring chamber is arranged with its longitudinal axis inclined relative to the longitudinal axis of a telescopic shock absorber, to be precise in such a manner that the two casing parts of the air spring, which are connected to one another by a U-bellows, are essentially coaxial with respect to one another. In order to be able to maintain this coaxiality, at least to a very great extent, even when suspension deflections occur, the lower casing part coupled to the telescopic shock absorber cylinder arranged at the bottom is connected in a laterally resilient manner to the cylinder by the interposition of an elastomeric shear spring arrangement, that is to say the lower casing part of the air-spring system can be displaced transversely to the axis of the telescopic shock absorber.
An object of the invention, then, is to provide, for air-spring legs of the type initially indicated above, an improved design in which the bellows are loaded distinctly more lightly in the radial direction.
This object is achieved according to the invention in that, by its end remote from the bellows, the casing part on the cylinder side is arranged for wobbling movement on the cylinder of the telescopic element.
The invention is based on the general principle of reducing the radial constraint of the air-spring bellows, or the buckling angle which may occur between the casing parts of the air chamber, by permitting a certain buckling movability between the cylinder and the casing part on the cylinder side, the casing part on the cylinder side always being forced into a central position by the bellows drawn taut by the pneumatic pressure in the air chamber, while undesirable displacements of the casing part on the cylinder side can be excluded.
The design according to the invention advantageously also permits the use of so-called singlelayer rubber bellows, in which only one single layer of threads, with the threads extending in the longitudinal direction, is provided. Bellows of this kind require an inner rolling surface substantially in the form of an outer cylinder, and also an outer rolling surface disposed at a radial distance therefrom and substantially in the form of an inner cylinder surface, that is to say the casing parts of the air chamber must axially overlap one another by means of correspondingly cylindrical parts, so that the bellows can be accommodated in the annular space between the cylindrical parts. In the arrangement according to the invention, with a casing on the cylinder side able to make wobbling movements, even with desirably shorter radial distances between the cylindrical rolling surfaces, it is possible for a collision between these cylindrical parts to be reliably avoided even when the telescopic element makes larger wobbling movements relative to the casing part on the piston side.
In principle, a design of this kind can also be advantageous for two-layer bellows.
Irrespective of the construction of the airspring bellows, the invention is therefore particularly suitable for designs having external guidance of the bellows in question.
In addition, it is advantageous that the ability of the casing part on the cylinder side to make wobbling movements can be achieved with very simple means. In accordance with an advantageous embodiment of the invention, it is possible to arrange on the cylinder of the telescopic element a flange-like collar on which the casing part on the cylinder side is supported for wobbling movement with the interposition of an annular part of elastomer material.
According to a particularly preferred embodiment, the flange-like collar may be in the form of an annular sector of a spherical surface and the casing part on the cylinder side can have a substantially matching annular spherical sector surface, so that the ring of elastomer material is arranged between a spherical outer surface and a spherical inner surface and, during wobbling movements of the casing part on the cylinder side, is subjected substantially only to shear stress.